奇特的一群：来自 Kepler 的十六颗异常恒星的年代学–化学–动力学研究
The odd bunch: chrono-chemo-dynamics of sixteen unusual stars from Kepler
AI总结：
本文结合星震、光谱与Gaia运动学分析Kepler场中16颗化学或年龄异常恒星，核查质量年龄并证实两颗古老超金属丰富巨星支持径向迁移。
摘要：
在本研究中，我们结合星震学、光谱学和运动学信息，对来自 Kepler 视场的一个包含16颗恒星的样本进行了详细分析。我们的选择重点关注那些似乎与银河系化学演化模型相矛盾的恒星：年轻且α元素丰富、年老且金属丰富，以及以往巡天中分类不明确的其他目标。运动学参数由 Gaia DR3 的视差和自行导出，并利用 HIRES/Keck 的高分辨率光谱计算20多种元素的化学丰度。这些信息被用于仔细核查通过基于网格的建模所得到的星震学质量和年龄。在此前被归类为年轻且α元素丰富的七颗恒星中，仅有一颗看起来明确是一颗掩盖了真实年龄的更年老天体。我们证实存在两颗非常年老（≥11 Gyr）、超金属丰富（≥0.1 dex）的巨星。这两颗恒星具有规则的薄盘化学特征和位于太阳圈内的平面轨道，这与通过搅动机制发生径向迁移的图像非常吻合。若用这些恒星年龄较小作为另一种解释，则需要质量损失率随金属丰度增加而显著上升。最后，我们建议进一步研究 Zn 作为红巨星化学时钟的适用性。
英文摘要：
In this study we combine asteroseismic, spectroscopic and kinematic information to perform a detailed analysis of a sample of 16 stars from the Kepler field. Our selection focuses on stars that appear to contradict Galactic chemical evolution models: young and $α$-rich, old and metal-rich, as well as other targets with unclear classification in past surveys. Kinematics are derived from Gaia DR3 parallaxes and proper motions, and high-resolution spectra from HIRES/Keck are used to calculate chemical abundances for over 20 elements. This information is used to perform careful checks on asteroseismic masses and ages derived via grid-based modelling. Among the seven stars previously classified as young and $α$-rich, only one seems to be an unambiguously older object masking its true age. We confirm the existence of two very old ($\geq$11 Gyr), super metal rich ($\geq$0.1 dex) giants. These two stars have regular thin disc chemistry and in-plane solar circle orbits which fit well in the picture of radial migration via the churning mechanism. The alternative explanation that these stars have younger ages would require mass-loss rates which strongly increases with increasing metallicity. Finally, we suggest further investigations to explore the suitability of Zn as a chemical clock in red giants.
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